Wastewater treatment facility recognized for sustainable infrastructure

by nithya_caleb | February 16, 2018 11:20 am

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Dixon’s[2] Wastewater Treatment Facility in California was honored by the Institute for Sustainable Infrastructure[3] (ISI) with an Envision[4] Silver award. The Envision rating system verifies the sustainability of infrastructure projects.

The City of Dixon’s Wastewater Treatment Facility Improvements project is the culmination of years of collaboration between the city, Stantec Consulting[5], California’s environmental regulators, and the public. Improvements to the facility address a range of community needs, goals, and issues, including:

• upgrading the aging wastewater treatment facility without an undue burden on ratepayers;
• meeting increased capacity demands; and
• addressing salinity limits placed on the facility by the state.

The Envision rating system is a collaboration between ISI and the Zofnass Program for Sustainable Infrastructure[6] at the Harvard University Graduate School of Design[7]. It measures sustainability in five categories:

• quality of life;
• leadership;
• natural world;
• resource allocation; and
• climate and risk.

The city of Dixon demonstrated leadership and a strong commitment to stakeholders by establishing a Wastewater Citizens Advisory Committee in 2007. The committee’s mandate was to determine viable options to address state-imposed sodium and chloride effluent limits while upgrading aging components of the existing facility that were unsafe and costly to maintain at or above their rated capacity. Options were put forward by the committee and evaluated by the city council. Once a decision was made, a public outreach program was initiated to inform and educate citizens on the project, including:

• incentives to remove salt-discharging water softeners;
• benefits of the selected treatment technology; and
• rate implications.

This outreach program helped address concerns and, ultimately, led to public and state regulatory approval of the facility improvements project. Additionally, the project team incorporated full life-cycle thinking to extend the project’s lifespan.

Robust nitrogen removal was included in the process because it saves energy and costs long term, and proactively addresses groundwater nitrate contamination, which has been identified as the largest long-term threat to groundwater drinking quality in agriculturally dominated areas worldwide, including the Central Valley of California.

The facility also implements a cost-effective and energy efficient method to minimize salinity impacts to groundwater. The facility’s large 52.6-ha (130-acre) treatment ponds were replaced with an oxidation ditch design having a significantly smaller exposed surface area. This reduces evaporative water losses by 100-fold. The retained water serves to keep the dissolved wastewater salts diluted, thereby reducing the effluent’s salinity.

By solving the salinity issues through evaporation reduction and an activated sludge process, the facility avoided conventional salt removal treatment methods (e.g. reverse osmosis and electrodialysis reversal) that are costly, consume significant amounts of energy, and produce a hazardous brine waste, which is expensive to manage in inland locations.

The project team conducted a comprehensive assessment of vulnerabilities that could create long-term costs and risks for the facility and the community it serves. Four specific risks were identified and mitigated by the design, including:

• potential seismic activity such as liquefaction and ground shaking;
• flooding and extreme rainfall events;
• long-term drought conditions and related water-supply shortages; and
• changing economic conditions.

Ultimately the project was designed to be resilient and adaptive to these potential changes in the operating environment over the course of its 50- to 100-year design life.

Source URL: https://www.constructionspecifier.com/wastewater-treatment-facility-recognized-sustainable-infrastructure/

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